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Seborrheic Keratosis

  • Appearance: sharply delineated, scaly or greasy, tan papules that appear “stuck on” the surface (Fig. 11-1)

  • Location: upper trunk, shoulder, face, and scalp (sun-exposed areas), but can occur anywhere (except palms and soles)

  • Demographics: more than 30 years

  • Histology: epithelial proliferations characterized by hyperkeratosis, papillomatosis, and acanthosis, with horn pseudocysts (called “pseudo” because they connect to surface, and they have no true epithelial lining)

  • Leser-Trelat syndrome: sudden onset of numerous seborrheic keratoses associated with internal malignancies, most commonly GI adenocarcinoma, breast carcinoma, and lymphoma

  • Variations

    • Inverted follicular keratosis: verrucous, intradermal or “inverted” form of irritated seborrheic keratosis along a hair follicle, with prominent squamous eddies

    • Dermatosis papulosa nigra: multiple small, pedunculated, and heavily pigmented tag-like papules on the face of African-American and Afro-Caribbean patients (Fig. 11-2)

    • Stucco keratosis (keratosis alba): white-to-light brown, flat keratotic papule on dorsa of feet, ankles, hands, and forearms

    • Melanoacanthoma: deeply pigmented seborrheic keratosis in which an epidermal proliferation of large dendritic melanocytes is identified

    • Acanthosis nigricans: hyperpigmented velvety plaques on neck and axillae associated with obesity, diabetes, and endocrinopathies; histology similar to seborrheic keratosis but no acanthosis

    • Confluent and reticulated papillomatosis (CARP): multiple brown verrucous papules in reticulated pattern on inframammary or interscapular trunk during puberty; histology similar to seborrheic keratosis but no acanthosis and pityrosporum can be identified

    • Lichenoid keratosis: solitary pink to red-brown papule on forearm or upper chest; may represent inflamed lentigo, actinic keratosis, or seborrheic keratosis


Seborrheic keratosis. (Used with permission from Dr. Asra Ali.)


Dermatosis papulosa nigra. (Used with permission from Dr. Asra Ali.)

Epidermal Nevus

  • Appearance: yellowish-brown warty papules or plaques (Fig. 11-3)

  • Location: usually trunk and extremities

  • Demographics: birth or during childhood

  • Characterization: congenital hamartoma (nevus) of epidermis

  • Three subtypes

    • Nevus verrucosus: solitary or multiple localized lesions

    • Nevus unius lateralis: extensive unilateral linear distribution

    • Ichthyosis hystrix: extreme involvement with bilateral or generalized distribution

  • Histology: hyperkeratosis, papillomatosis, acanthosis, and elongation of the rete ridges

  • Syndromes

    • Epidermal nevus syndrome: skeletal, ocular, and central nervous system (CNS) abnormalities

    • Nevus comedonicus syndrome: nevus comedonicus with cutaneous, skeletal, and CNS abnormalities

  • Variations

    • Nevus sebaceus: see Sebaceous Tumors

    • Linear porokeratosis: see Porokeratosis

    • Linear epidermal nevus: verrucous yellow-brown papules in a linear arrangement (systemic form follows Blaschko lines) due to heterozygous point mutation in the keratin 10 gene; histologically resembles nevus sebaceus with focal epidermolytic hyperkeratosis and lack of adnexal components

    • Nevus comedonicus: group of open comedones on face, trunk, neck, and upper extremities; keratin-filled invaginations of the epidermis


Epidermal nevus. (Used with permission from Dr. Asra Ali.)

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